Equações básicas - exemplos resolvidos

Q 1 - Se 8x + 5y = 9 e 3x + 2y = 4, o que é y?

A - 5

B - 6

C - 7

D - 8

Answer - A

Explanation

The given equations are:
8x+5y = 9 ...(a)
3x+2y = 4 ...(b)
On multiplying (a) by 2, (b) by 5 and subtracting, we get: x= -2
Putting x = -2 in (b), we get:
-6 + 2y = 4 => 2y = 10 ∴ y = 5

Q 2 - Se 5 / x + 6y = 13 e 3 / x + 4 = 7, encontre o valor de y.

A - 0

B - -1

C - -2

D - -3

Answer - C

Explanation

The given equation is:
5/x +6y = 13 ...(a)
3/x+4y =7 ...(b)
On multiplying (a) by 3, (b) by 5 and subtracting, we get:
-2y = 4 ∴ y = -2

Q 3 - Dado (x + y-8) / 2 = (x + 2y-14) / 3 = (3x + y-12) / 11. Então x, y são

A - 1,7

B - 2,7

C - 2,6

D - 1,5

Answer - D

Explanation

Taking first two parts, we get:  
(x+y-8)/2 = (x+2y-14)/3   
=> 3 (x+y-8) = 2(x+ 2y-14)
=> 3x+3y-24 =   2x+4y -28
=> x- y= -4 ...(1)
Taking last two parts, we get:
(x+2y-14)/3 = (3x+y-12)/11 
=> 11 (x+2y-14) = 3(3x+y-12)
=> 11x+ 22y - 154 = 9x+3y -36
=> 2x+19y- 118 ...(2)
Multiplying (1) by 2 and subtracting from (2) we get,
21 y = 126 
=> y = 6
Putting y = 6 in (1), we get: x= 2
=> x= 2, y= 6

Q 4 - Dado 217x + 131y = 913 e 131 x + 217 y = 827. Então x, y são

A - 1,6

B - 3,2

C - 12,13

D - 16,18

Answer - B

Explanation

217x +131y= 913  ...(a)
131 x+ 217 y= 827 ...(b)

It is a special case in which coefficients of x and y in (a) are interchanged in (b)
Adding (a) and (b) , we get : 348(x+y)= 1740 => x+y = 5 ...(a)
Subtracting (b) from (a), we get: 86(x-y) = 86 => x-y =1 ...(b)
Adding (a) and (b), we get: x= 3, y= 2

Q 5 - Para qual valor de h, o sistema de equações, hx-y-2 = 0 e 6x-2y-3 = 0 tem uma solução única?

A - 2

B - 3

C - 4

D - 5

Answer - B

Explanation

For, a unique solution, we must have a1/a ≠ b1/b2
h/6 ≠ -1/-2 =>  h/6 ≠ 1/2 => h = 3

Q 6 - Para qual valor de h, o sistema de equações, x + 2y + 7 = 0 e 2x + hy + 14 = 0 tem um número infinito de soluções?

A - 3

B - 4

C - 5

D - 6

Answer - B

Explanation

For infinite solutions, we have a1/a2 = b1/b2= c1/c2;
h1/2 = 2/h = 7/14 => h=4.

Q 7 - Para qual valor de h, o sistema de equações, hx-10y-3 = 0 e 3x-5y-7 = 0 não tem solução?

A - 6

B - 5

C - 4

D - 3

Answer - A

Explanation

For no solution, we have a1/a2 = b1/b2 ≠ c1/c1
∴ h/3 = -10/-5 ≠-3/-7 => h = 6